An eight-year journey through the inner Solar System is approaching its final destination as the European-led BepiColombo probe prepares for orbital insertion at Mercury. Led by the European Space Agency alongside partners in Japan and the United States, the nearly $2 billion robotic endeavor passed a crucial milestone this week during its final approach to the scorched, iron-rich world.
Since setting off in 2018, the spacecraft has navigated a complex spiral trajectory toward the Sun. Rather than traveling directly, BepiColombo has relied on a hybrid navigation strategy that combines plasma thrusters with a sequence of gravitational flybys utilizing Earth, Venus, and Mercury itself. These delicate maneuvers have progressively trimmed the craft's speed, positioning it for a final rendezvous scheduled for later this year.
Reaching the Solar System's innermost planet requires extraordinary energy. Despite Mercury being much closer to Earth than distant targets like Pluto, achieving orbit around the swift planet demands more velocity change—known as delta-v—than sending a probe on a flyby to the outer solar system. For comparison, NASA's New Horizons spacecraft spent almost ten years traveling to Pluto, yet required less overall energy for its flyby than BepiColombo needs to brake into Mercury's gravitational pull.
When BepiColombo makes its next encounter later this year, it will finally be traveling at the precise speed necessary for Mercury's gravity to capture the probe into orbit. The upcoming event represents the long-awaited climax for interplanetary scientists accustomed to spending decade-long spans waiting for mission payoffs.
